WO2007094255A1

WO2007094255A1 - D/a converter

Info

Publication number: WO2007094255A1
Application number: PCT/JP2007/052351
Authority: WO
Inventors: Shinichi Harigae
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2006-02-14
Filing date: 2007-02-09
Publication date: 2007-08-23
Also published as: EP1988635A1; US7817074B2; US20090027248A1; JPWO2007094255A1; JP4699510B2

Abstract

A D/A converter (100) comprises a delta-sigma modulating circuit (102) including a quantizer (105) that receives a digital signal to quantize it based on a quantizing reference value; a local D/A converting circuit (107) for converting an output from the delta-sigma modulating circuit to an analog signal to be outputted; and a control circuit (109) for correcting the quantizing reference value of the quantizer. The quantizing reference value is established for each of a plurality of discrete output values that the quantizer may output. The control circuit (109) corrects the quantizing reference value to cancel any distortion that would otherwise occur in a circuit that follows the delta-sigma modulating circuit (102) and that includes at least the local D/A converting circuit (107).

Description

Specification

DZA converter

Technical field

The present invention relates to a DZA converter for converting a digital signal into an analog signal, and more particularly to a DZA converter having a delta sigma modulation circuit.

Background art

[0002] Conventionally, a DZA converter using a delta sigma modulation circuit is known as a means for converting a digital signal into an analog signal. An example of a conventional DZA converter is shown in FIG. In FIG. 5, a digital input 401 is PCM data of a long word length, for example, 16 bits. The digital input 401 is noise shaved by the delta sigma modulation circuit 402 and converted into several bits of digital data. The output of the delta sigma modulation circuit 402 becomes an analog output 408 by the local DZ A conversion circuit 407.

As an internal operation of the delta sigma modulation circuit 402, a digital input 401 is added to a negative feedback signal from a delay unit 406 in a calo calculator 403, and is further integrated in an integrator 404. The output of the integrator 404 is requantized to about several bits by the quantizer 405 and input to the local DZA conversion circuit 407. Also, the output of the quantizer 405 is input to the delay unit 406 as a feedback signal.

The quantizer 405 requantizes the input digital value in accordance with the quantization reference value.

The quantization reference value is set corresponding to the quantization value which is a discrete value that the quantizer 405 can output. Figure 6 shows the input / output characteristics of the conventional DZA variation 100b quantizer 405. In the figure, “図” indicates a quantization reference value. In the figure, the quantizer 405 requantizes the input into five steps of + 2−−2. Also, the quantization reference values for these five values have linear characteristics (see dashed line X). For example, when the input to the quantizer 405 is M, the output of the quantizer 405 is 1, and the quantization error at this time is 0. Similarly, when the input to the quantizer 405 is 2M, the output of the quantizer 405 is 2, and the quantization error at this time is 0. Further, the threshold level between adjacent quantization values is an intermediate value with respect to the quantization reference value. For example, the threshold value of quantization value 0 and quantization value 1 is MZ2. In general, it is desirable that distortion does not occur in the signal propagation path in DZA modulation ^^, but in fact, distortion occurs in the local DZA conversion circuit or in an analog circuit connected after the local DZA conversion circuit. Occur. Hereinafter, distortion generated when a pulse width modulation circuit is used as the local DZA conversion circuit 407 will be described.

The pulse width modulation circuit 407 converts a digital signal of several bits into two values (1 bit) of H level and L level. It is ideal that the binarized signal is a signal as shown in FIG. 7 (a), but actually it is shown in FIG. 7 (b) due to the influence of analog factors such as wiring impedance. Such waveform distortion occurs. The occurrence of such waveform distortion degrades the characteristic of the analog output for each value of the output of the quantizer 405. That is, an ideal analog output has a characteristic showing linearity with respect to a quantizer output (input to the pulse width modulation circuit 407), but an actual analog output shows a non-linear characteristic.

[0007] In order to solve this problem, for example, a signal amplification apparatus as shown in Patent Document 1 has been proposed. According to Patent Document 1, the distortion amount is calculated from the rising difference and the falling difference between the pulse width modulated signal and the signal obtained by amplifying the pulse width modulated signal to a predetermined size, and the distortion is calculated. Distortion is reduced by subtracting the amount from the quantizer output.

Patent Document 1: Japanese Patent Application Laid-Open No. 2003-110376

Disclosure of the invention

Problem that invention tries to solve

However, while the signal amplification device of Patent Document 1 requires level change, the number of parts in the entire circuit increases, the manufacturing cost increases, and the mounting area increases. It had the problem of.

Furthermore, if the amount of distortion is large, the amount of correction added to the feedback loop may be large and oscillation may occur. In order to prevent this oscillation, if the gain of the delta sigma modulation means is reduced on the assumption that the distortion amount is large and the case is taken into consideration, there is a problem that the signal amplification rate becomes small when the distortion amount is small. The

An object of the present invention is to provide a DZA variation that achieves a high signal amplification factor without causing any distortion and causing less distortion and an increase in circuit scale. Means to solve the problem

In the DZA transformation according to the present invention, a digital signal is input, and a delta sigma modulation circuit including a quantizer that quantizes based on a quantization reference value and an output of the delta sigma modulation circuit are converted to an analog signal. And a control circuit that corrects the quantization reference value of the quantizer. A quantization reference value is set for each of a plurality of discrete output values that the quantizer can output. The control circuit is connected to the subsequent stage of the delta sigma modulation circuit, and corrects the quantization reference value so as to cancel distortion generated in the subsequent stage circuit including at least the local DZA conversion circuit.

That is, assuming that the quantization reference value of the quantizer corresponding to the output value N of the quantizer is M and the ideal analog output signal value for the output value N of the quantizer is P, then When the actual analog output signal power SP X α is obtained with respect to the analog output signal value P, the effects of this distortion are canceled, and quantization is performed so that the resulting actual analog output signal becomes Ρ. The reference value is corrected to MX a.

Effect of the invention

According to the DZA converter of the present invention, distortion can be reduced simply by setting the quantization reference value of the quantum inductor by the control circuit without requiring an additional circuit such as a level converter. As well as suppressing an increase in circuit scale, a high signal amplification factor can be secured.

Brief description of the drawings

FIG. 1 is a diagram showing the configuration of a DZA converter according to the present invention.

[Figure 2] Figure showing the characteristics of the input and output of the local DZA conversion circuit and the analog circuit after it

[FIG. 3A] A diagram showing input / output characteristics of the quantizer before the quantization reference value correction according to the present invention

[FIG. 3B] A diagram showing input / output characteristics of a quantizer after quantization reference value correction according to the present invention. [4] A diagram showing the configuration of a local DZA conversion circuit capable of outputting multistage pulse signals

[Figure 5] Diagram showing the configuration of a conventional DZA converter

[Figure 6] A diagram showing the input and output characteristics of a conventional quantizer

[Figure 7] Output waveform diagram of the local DZA conversion circuit Explanation of sign

[0015] 101 digitizer input

102 Delta sigma modulation circuit

103 Adder

104 integrator

105 Quantizer

106 delay device

107, 107b Local DZA conversion 1

108 Analog output

109 Control circuit

401 digitizer input

402 Delta sigma modulation circuit

403 Adder

404 integrator

405 Quantizer

406 Delay

407 Local DZA Converter

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the DZA variation according to the present invention will be described with reference to the attached drawings.

FIG. 1 is a block diagram showing an embodiment of the DZA variant of the present invention. The DZA converter 100 includes a delta sigma modulation circuit 102 that delta sigma modulates an input signal, a control circuit 109 that controls the quantization operation of the digital sigma modulation circuit 102, and PWM (Pulse Width Modulation) of the output of the delta sigma modulation circuit 102. B.) A local DZA conversion circuit 107 that modulates and outputs as an analog output. The digital sigma modulation circuit 102 includes an adder 103, an integrator 104, a quantizer 105, and a delay unit 106.

The delta sigma modulation circuit 102 receives, as an input signal, a digital input 101 which is long word length, for example, 16-bit PCM data. In the delta sigma modulation circuit 102 , Digital input 101 is summed with the negative feedback signal from delay 106 by summer 103 and then integrated by integrator 104. The output of the integrator 104 is input to the quantizer 105 and requantized by the quantizer 105. The output of the quantizer 105 is input to the local DZA conversion circuit 107. The local DZA conversion circuit 107 PWM modulates the output of the quantizer 105 and outputs it as an analog output 108.

The quantizer 105 will be described. The quantizer 105 converts the input digital value (the output of the integrator 104) into discrete value quantization values in accordance with the quantization reference value and outputs the result. In this example, the quantizer 105 performs requantization to convert 16-bit data into 3-bit data. The quantization reference value is set corresponding to each quantization value. The quantization reference value is equal to the input value of the quantizer 105 when the quantization error is quantized at zero. The error between the input value of the quantizer 105 and the quantization reference value is fed back, added to the digital input value 101 of the next period, and the quantizer 105 adds the error to the digital input value. Requantization is performed. Therefore, by varying the quantization reference value, the input / output characteristics of the quantizer 105 are varied.

Next, setting of a quantization reference value of the quantizer 105 of the present embodiment will be described. The quantization reference value of the quantizer 105 is corrected (adjusted) by the control circuit 109. In particular, in the present embodiment, the quantization reference value of the quantizer 105 is determined in consideration of the distortion characteristic that may occur in the local DZA conversion circuit 107 and the analog circuit in the subsequent stage.

In the present embodiment, the quantizer 105 requantizes into 2-step 5-step quantization values (output of the quantizer 105). The quantization reference value of the quantizer 105 is set so that the input / output characteristics become linear as shown in FIG. 3A in the initial state. That is, in the quantizer 105, "M" is set as the initial value of the quantization reference value for the quantization value "1", and "2M" is set as the initial value of the quantization reference value for the quantization value "2". I see. After the quantization reference value of the quantizer 105 is corrected by the control circuit 109, the DZA variation 100 becomes usable. The correction of the quantization reference value will be described below.

FIG. 2 is a diagram showing input / output characteristics of the local DZA conversion circuit 107 and an analog circuit (not shown) in the subsequent stage. That is, from FIG. 2, it is possible to understand the characteristics of distortion that may occur in the local DZA conversion circuit 107 and its subsequent analog circuit. In the same figure, The symbol "A" indicates an ideal analog output, and the symbol "B" indicates an actual analog output including distortion. As shown in the figure, the ideal characteristic (broken line Y) indicates linearity. For example, the ideal analog output value corresponding to the output value “1” of the quantizer 105 is “P”. The actual analog output is a smaller value than the ideal analog output value P “ PX α is a positive number less than 1). Similarly, the ideal analog output value corresponding to the output value “2” of the quantum device 105 is “2Ρ” The actual analog output is “2Ρ 、 (β is a positive value less than 1 The number of

Here, in accordance with the ideal characteristic (broken line Υ), the output value of the quantizer corresponding to the analog output value “Ρ X α” is “α”. On the other hand, when the quantization reference value for the output (quantization value) “1” of the quantizer 105 is “Μ” as shown in FIG. 3Α, the quantization reference value corresponding to the quantization value “ひ” is It becomes "Μ α α". From this, it can be considered that the actual analog output value "できる見なす α" is an ideal analog output value when the quantization reference value is multiplied by oc. That is, when the actual analog output is multiplied by a with respect to the ideal analog output due to distortion, the quantization reference value “M” corresponding to the quantization value “1” is multiplied by oc and corrected. The quantization value is virtually multiplied by α α, but then it is multiplied by α by distortion of the analog circuit, which indicates that distortion can be finally canceled. Similarly for the quantization value "2", when the actual analog output is multiplied by j8 with respect to the ideal analog output "2Μ", the quantization reference value corresponding to the quantization value "2" is The distortion can be canceled by setting “2 Χ」 ”. In this way, the quantization reference value for each quantization value is corrected based on the actual analog output characteristics corresponding to all the quantization values.

FIG. 3B shows the input / output characteristics of the quantum integrator 105 whose quantization reference value has been corrected by the control circuit 109 as described above. In the figure, “図” indicates a quantization reference value. As shown in FIG. 3B, the quantization reference value for the quantization value “1” is corrected to “Μα”, and the quantization reference value for the quantization value “2” is corrected to “2Μ”. The other quantization reference values are similarly corrected in consideration of the distortion characteristics of the analog circuit. In FIG. 3A, when the input value of the quantizer 105 is “Μ ひひ”, the output of the quantizer 105 is “1”. At this time, since the input value of the quantizer 105 is equal to the quantization reference value “Μ ひひ”, no quantization error occurs. Also, referring to FIG. 2, the quantizer output value “1” becomes the actual analog output value “Χ ひひ”. Therefore, the amplification factor is PZM (= (PX α) / (Μ α α)). Similarly, in FIG. 3A, when the input value of the quantizer 105 is “2M X j 8”, the output of the quantizer 105 is “2”. At this time, since the input value of the quantizer 105 is equal to the quantization reference value “2M X”, no quantization error occurs. Further, referring to FIG. 2, since the quantizer output value "2" is the actual analog output value "2 PX j8", the amplification factor is PZM (= (2P X j8) Z (2M X j8)) . As described above, since the amplification factor always shows a constant, the analog output shows a linear shape, and the distortion is reduced.

When the correction amount becomes large with respect to the corrected quantization reference value, that is, when the generated quantization error is corrected to increase, oscillation may occur. Therefore, in order to prevent the oscillation, the control circuit 109 may further correct the multiplied quantization reference value after correction by multiplying it by a constant A. As a result, it is possible to realize the quantizer 105 having a high amplification factor while suppressing the oscillation. Here, the constant A is based on the maximum value X of the quantization error before correcting the quantization reference value and the maximum value y of the quantization error after correcting the quantization reference value, and A = yZx It is calculated. However, depending on the configuration of the delta sigma modulation circuit, it may be determined by another appropriate calculation method beyond this limit.

Further, it is desirable that the threshold value of each adjacent quantization value be a midpoint between the adjacent quantization reference value so that the quantization error can be suppressed to a fixed amount. However, an appropriate threshold may be set according to the characteristics of the feedback circuit in the delta sigma modulation circuit.

The distortion characteristics of the analog output may be calculated by separately adding a circuit for measuring the characteristics, but measuring the characteristics by using a measuring instrument in advance will measure the characteristics. , But also. According to the configuration, the control circuit 109 causes the quantizer 105 to correct the distortion generated by the local DZA conversion circuit 107 and the circuit connected to the subsequent stage in advance. By setting the conversion reference value, parts such as level change ^ can be eliminated, and distortion can be reduced at low cost.

In addition, although the first-order delta sigma modulation circuit is used in the present embodiment, the second-order or higher-order delta sigma modulation circuit may not be limited to this. .

Further, in the present embodiment, the distortion characteristic that may occur in local DZA conversion circuit 107 and the ana- ger circuit at the subsequent stage is taken into consideration. However, distortion that may occur in local DZA conversion circuit 107 Let's correct the quantization reference value by considering only the characteristics of the image.

Further, the local DZA conversion circuit 107 is not limited to the above-described PWM modulation circuit. FIG. 4 shows another configuration of the local DZA conversion circuit connected to the rear stage of the DZA converter 100 of the present embodiment. The local DZA conversion circuit 107 b shown in FIG. 4 includes a decoder 702, a pulse generator 703, and an adder 704. The decoder 702 receives the digital value 701 quantized from the DZA transformation 100, decodes the digital value 701, and generates two types of decoded signals S1 and S2. The decoded signals S1 and S2 are generated by decoding the upper bits and the lower bits of the digital value 701, for example. The pulse generator 703 generates pulse signals P1 and P2 which are PWM-modulated corresponding to the decode signals S1 and S2, respectively. The peak values of the pulse signals P 1 and P 2 are made different. The adder 704 adds the pulse signals P1 and P2 and outputs the result as an analog output 705. The distortion of the input / output characteristics of the local DZA conversion circuit 107b shown in FIG. 4 is measured, and the quantization reference value of the quantizer 105 is corrected to cancel the distortion, thereby causing the local DZA conversion circuit 107b. You can cancel the distortion. Industrial applicability

The DZA transformation of the present invention enables distortion reduction with an easy circuit configuration, and is useful for DZA transformation used in audio equipment and the like.

Although the present invention has been described with respect to particular embodiments, many other variations, modifications, and other uses will be apparent to those skilled in the art. Therefore, the present invention is not limited to the specific disclosure herein, but may be limited only by the appended claims. The present application is related to Japanese Patent Application No. 2006-036284 (filed on February 14, 2006), the contents of which are incorporated herein by reference.

Claims

The scope of the claims

[1] A delta sigma modulation circuit including a quantizer that inputs a digital signal and quantizes based on a quantization reference value,

A local DZA conversion circuit which converts the output of the delta sigma modulation circuit into an analog signal and outputs it;

A control circuit for correcting a quantization reference value of the quantizer;

The quantization reference value is set for each of a plurality of discrete output values that can be output by the quantizer.

The control circuit corrects a quantization reference value of the quantizer so as to cancel distortion generated in a circuit connected to a subsequent stage of the delta sigma modulation circuit. DZA variation.

[2] The amount of the quantizer when the output of the circuit connected in the latter stage is multiplied by α with respect to the ideal output value due to distortion caused by the circuit connected in the latter stage. 2. The DZA variation according to claim 1, wherein the quantization reference value is corrected by multiplying the aging standard value by α.

[3] The control circuit sets the threshold of the range of the input value of the quantizer, which is set corresponding to each of the discrete output values of the quantizer, to an intermediate value between the adjacent quantization reference values. The DZA converter according to claim 1, wherein the DZA converter is set to.

[4] The DZA converter according to claim 1, wherein the control circuit further multiplies the corrected quantization reference value by a constant Α.

[5] The constant A is based on the maximum value X of the quantization error before correcting the quantization reference value and the maximum value y of the quantization error after correcting the quantization reference value, A = yZx The DZA converter according to claim 4, calculated by

[6] The DZA converter according to claim 1, wherein a circuit connected to a subsequent stage of the delta sigma modulation circuit includes the local DZA conversion circuit.

7. The DZA converter according to claim 1, wherein the local DZA conversion circuit is a pulse width modulation circuit that generates a pulse signal whose pulse width is modulated according to a digital output from the delta sigma modulation circuit. 2. The pulse width modulation circuit according to claim 1, wherein the local DZA conversion circuit is a pulse width modulation circuit that generates a multistage pulse signal having a plurality of pulse signal powers pulse width modulated according to a digital output from the delta sigma modulation circuit. DZA converter.